Focal point

Definition

The focal point is the specific point on either side of a lens or mirror where parallel light rays converge or appear to diverge from.

Analogy

Think of your bedroom window on a sunny day. When sunlight passes through your window blinds, you may notice that all those parallel beams of light meet at one spot on your floor. That spot where they converge is similar to what we call the focal point.

Related terms

Lens equation: The mathematical relationship between an object's distance from a converging (convex) or diverging (concave) lens, its image distance, and their respective focal lengths.

Principal axis: An imaginary line that passes through both sides of an optical device (such as lenses or mirrors), perpendicular to their surfaces.

Ray diagram: A visual representation used to determine how light rays interact with lenses or mirrors and predict where images will form.